Right-click your Contacts folder, choose Properties, click the Outlook
Address Book tab, and check the box labeled "Show this folder as an e-mail
Address Book".  Click OK.  (At this point, I'd stop and restart Outlook, but
I'm not positive it's required.)  Now click the Address Book button and
click Tools>Options.  Adjust which folder you want to see first in the "Show
this address list first" drop-down and the search order Outlook will use
when resolving addresses in the "When sending..." pane in the lower half of
the dialogue.  Click OK.  You can close the address book view as well.